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Attic ventilation & cellulose

user-6603947 | Posted in Energy Efficiency and Durability on

I have a multi-level home in Lincoln, NE (zone 5). Half the roof is a traditional vented attic; the other half has vaulted ceilings with 2×6 rafters (assuming R-19 batts) on the lower half of the roof, then a vented attic on the top half. The vented attics have blown-in cellulose about 11″ deep (~R-35). I’ve already air-sealed all the ceiling cracks and electrical boxes with caulk and spray foam, and I am planning to add more cellulose in the spring. There are a couple items I need to address first:

1) Per code, my current attic ventilation is insufficient. I have adequate NFVA at the ridge, but I need about 50% more soffit ventilation to meet code. The builder also chose to install cheap plastic baffles about every 3rd or 4th rafter bay (I was under the assumption that every bay should have a baffle).

While our home may not be up to snuff per code, I have not witnessed any of the typical attic ventilation problems. We do not have an issue with ice dams, & I have been in the attic a couple times during the last 4 winters without any sign of frost or condensation on the underside of the sheathing. I also took photos of the roof and our 2nd floor ceilings using a thermographic camera; the only hot spot I found was in the rafter bay where our furnace flue comes up, so nothing out of the ordinary. If we are not experiencing any issues, is there any reason to believe additional soffit ventilation would provide any benefit?

2) I have blown in cellulose in the past, and I my biggest weak spot was ensuring adequate coverage at the eaves. I tried to blow it in tight at the eaves, but with the dust created, I couldn’t see how well it had filled. After I took the machine back and the dust settled, I realized I did a poor job. This time, I was planning to pile the existing insulation in front of the eaves then take a broom handle to pack the existing cellulose in tight above the top plate and up to my desired 16-17″ height. Then when I blow in the additional cellulose, I won’t have to worry about visibility when the dust starts flying. Any better ideas? Do you think packing cellulose at the eaves may exacerbate the soffit ventilation issue?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Derrick,
    Q. "If we are not experiencing any issues, is there any reason to believe additional soffit ventilation would provide any benefit?"

    A. Better ventilation channels aren't necessary for your attic -- but they are essential for your cathedral ceilings, and if they are missing, you may have a big problem. Here are links to relevant articles:

    All About Attic Venting

    How to Build an Insulated Cathedral Ceiling

  2. GBA Editor
    Martin Holladay | | #2

    Derrick,
    You may want to read these two articles:

    Borrowing a Cellulose Blower from a Big Box Store

    How to Install Cellulose Insulation

    Q. "I was planning to pile the existing insulation in front of the eaves then take a broom handle to pack the existing cellulose in tight above the top plate and up to my desired 16-17" height. Then when I blow in the additional cellulose, I won't have to worry about visibility when the dust starts flying. Any better ideas?"

    A. I like to use a garden rake instead of a broom handle for this task.

    Q. "Do you think packing cellulose at the eaves may exacerbate the soffit ventilation issue?"

    A. No, as long as you have ventilation baffles that extend to a height that is several inches above the top of the cellulose. For more information, see Site-Built Ventilation Baffles for Roofs.

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